Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically use various techniques, such as layering, doping, masking, and etching, to build thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together with aluminum wires to define a specific electric circuit, such as a computer memory.
To form the aluminum wires, fabricators sometimes use a dual-damascene metallization technique, which takes its name from the ancient Damascan metalworking art of inlaying metal in grooves or channels to form ornamental patterns. The dual-damascene technique entails covering the components on a wafer with an insulative layer of silicon dioxide, etching small holes in the insulative layer to expose portions of the components underneath, and subsequently etching shallow trenches from hole to hole to define a wiring pattern. Fabricators then blanket the entire insulative layer with a thin sheet of aluminum and polish off the excess, leaving behind aluminum vias, or contact plugs, in the holes and thin aluminum wires in the trenches. The aluminum wires are typically about one micron thick, or about 100 times thinner than a human hair.
In recent years, researchers have begun using copper instead of aluminum to form integrated-circuit wiring, because copper offers lower electrical resistance and better reliability at smaller dimensions. See, for example, D. Edelstein et al., Full Copper Wiring in a Sub-0.25 um CMOS ULSI Technology, Technical Digest of 1997 IEDM, p. 773-776, 1997; and S. Venkatesan et al., A High Performance 1.8V, 0.20 um CMOS Technology with Copper Metallization, Technical Digest of 1997 IEDM, p. 769-772, 1997. Moreover, Applied Materials, Inc., a maker of semiconductor fabrication equipment, reports special equipment for fabricating copper-wired integrated circuits. (Applied Materials Announces First Barrier/Seed Layer System for Copper Interconnects, http://www.appliedmaterials.com/newsroom/pr-00103.html, Dec. 2, 1997.)
These copper-wired integrated circuits typically follow a variation of the dual-damascene method, which entails forming a copper-diffusion barrier in holes and trenches prior to filling them with copper. The typical copper-diffusion barrier is more than 30-nanometers thick and consists of tantalum (Ta), tantalum nitride (TaN), tantalum silicon nitride (TaSiN), titanium nitride (TiN), or tungsten nitride (WN). Filling the barrier-lined holes and trenches with copper generally entails forming a thin copper seed layer on the copper-diffusion barrier and then electroplating copper on the seed layer to finish.
The present inventors identified at least two problems with current techniques for making the copper wiring. The first is that typical copper-diffusion barriers add appreciable resistance to the copper wiring, and thus negate some of the advantages of using copper. The second concerns the use of separate wafer-processing chambers to form the copper-diffusion barrier and the copper seed layer. Using two chambers means that wafers are processed in one chamber to form the diffusion barrier and then transported to another chamber to form the seed layer. However, moving wafers from one chamber to another not only slows down fabrication, but also risks the addition of undesirable particles to the wafers, some of which can cause defects in resulting integrated circuits.
Accordingly, there is a need for better ways of making copper wiring in integrated circuits.